1. Field of the Invention
The present invention relates to fluid treatment systems, and more particularly, to water treatment systems utilizing a bed of particulate treatment material and having apparatus for regenerating the treatment material.
2. Prior Art
Many large, commercial water treatment systems of the ion exchange type presently in use are constructed to receive untreated water through an inlet line in the top of a pressure tank so that it percolates downwardly through a bed of treatment material, such as zeolite, and passes out of the pressure tank through an outlet line originating in a lower portion of the tank. The outlet line preferably consists of a central distribution tube, mounted within the pressure tank, and a plurality of distributor conduits extending outwardly from a lower end of the central distribution tube and terminating in distributors. The distributors are generally hollow and cylindrical in shape, and have perforations in their walls to permit the entry of water from the pressure tank while preventing the entry of the treatment material. As the untreated water percolates through the bed of treatment material, an ion exchange takes place in which ions held by the treatment material are exchanged for ions in the untreated water. It is important that the flow resistance provided by the overall system during normal operation be kept to a minimum so that the pressure of the treated water does not drop below a minimum pressure level.
The water treating ability of the treatment bed is gradually reduced by continued use and, after a predetermined quantity of water has been treated, the treatment material in the bed becomes depleted and is no longer able to effect an ion exchange. The treatment bed is thereafter regenerated by passing a fluid solution through it so that the ion exchange process is reversed: the ions held by the spent treatment material which had been received from the water are exchanged for ions suspended in the regenerating fluid solution.
Prior to the regeneration cycle of a typical water softening system, the system undergoes a backwashing cycle in which water, which may be hard, soft, or decationized, enters the pressure tank through the central distribution tube and exits the distributors to percolate upward and leave the pressure tank through the inlet line. This flow of water from the distributors upwardly causes the treatment material to be agitated, which loosens the packed treatment material and forces deposits of debris previously carried into the pressure tank from the inlet line to migrate upwardly through the treatment bed and out the inlet line. The loosened material can be regenerated more thoroughly.
To provide a thorough removal of accumulated debris from the treatment bed during this backwashing cycle, it is important that the entire resin bed be agitated. However, if the distributors are placed at different levels within the pressure tank, or where debris has accumulated to a greater degree around one or more of the distributors than around the remaining distributors, the resistance to fluid flow from the central distribution tube through the distributors becomes unequal. As a result, fluid flow through the distributors from the central distribution tube is unequal, as the water follows the path of least resistance. Since fluid flow through those distributors having the greatest resistance is the least, the treatment material surrounrding those distributors is agitated less than the treatment material around the other distributors having relatively little resistance. Consequently, accumulated debris is not removed as thoroughly from the treatment material having heavier soil concentrations as it is from treatment material having lighter concentrations of soil.
Accordingly, there is a need for a water treatment system which compensates for the variance in resistance to fluid flow through the distributors during a backwash cycle so that the fluid flow through each distributor is not reduced substantially as a result of debris concentration, whereby all portions of the treatment bed may be agitated sufficiently.